How far you need to see will determine what security camera lens you should use to best fit your application. A 4mm lens will give about a 70 degree angle of view with 35 feet of facial detail. This works great for residential or small office security camera applications. If you need to see further you would go with a higher powered lens. Keep in mind that the further you want to see will narrow the field of view of your picture.
Click here to use our Lens Calculator Tool. This tool will help you calculate the field of view you will get with a particular lens. Or you can calculate the required lens size needed to obtain a particular field of view.
A rule of thumb is that a 8mm lens is like a 4mm lens zoomed in 2 times. Similarly, a 16mm lens is like the 4mm lens zoomed in 4 times. For example, a 16mm lens would give you about a 15 degree angle of view focused at 35 ft.
Instead of going with a fixed focus lens you can go with a varifocal lens. With a simple adjustment you can manually zoom in or zoom out and focus the camera to the exact distance needed to get a clear picture. Varifocal lenses come in all different sizes: (3.5-8mm; 9-22mm; and 5-50mm) just to name a few. This is the best option for large commercial applications because you can adjust the focal distance to what works just right.
A Pan Tilt Zoom camera (PTZ) allows you to pan (back and forth), tilt (up and down), and zoom (focus in and out) your camera remotely. The PTZ is controlled using a remote PTZ controller or you can control it through most DVRs (look for PTZ support). The disadvantages of a PTZ camera is that they are very expensive (usually around $1000 without the controller). And all the moving parts make it susceptible to wear and breakdown. There are some new digital versions of PTZ cameras just coming on the market that have no mechanical parts. These PTZs are very promising but are still a little too expensive to be practical for most uses. PTZ cameras require a data cable to be run to the camera in addition to the video and power cables. Unless you have a person who is watching the scene and adjusting the field of view of the camera based on whats going on its not as useful. Most times you are better off buying more of the non-PTZ cameras to continuously cover the area rather than a PTZ.
The iris controls how much light is let into the camera lens. In the old days, cameras came with no iris control. If you needed to control the light levels you would have to purchase a special lens. Nowadays, most cameras come with automatic shutters which perform the same function as the iris – controlling how much light is let into the camera. Unless you have an application with extreme light levels (like at a beach) you probably won’t need a special lens with iris control.